Thanks for the replies.
After a bit of an experiment it seems I may have got this wrong

I thought that I could control the hot water independantly, but it
seems that I can switch it ON indepedantly, but if I switch the
central heating on then the hot water is on anyway...

It just seemed a bit of a waste leaving the hot water "reheating" all
day... and the water gets VERY hot... after climbing around in the
airing cupboard and ripping up a floorboard it seems my system is
setup a little differently than I thought... I thought I had one of
these Y designs that had a valve somewhere between the boiler and the
hot water tank, but the only thing I can find is the pump (above the
boiler).. no valves anywhere (unless it is under the floorboards in
the hall).

Anyway, the hot water is very hot and I found the temperature setting
on the hot water tank, it's set to 70 deg C so I might lower that to
60 deg C.

Doesn't seem worthwhile ripping out the pipes and connecting a valve
and a new programmable timer.
Seems I have 3 options
1. live with it and see how much the gas bill is after winter.
2. get a combi boiler installed (can't really afford this at the
moment)
3. get a programmable stat (thanks for the suggestion, didn't know
about them)

One possible solution to your requirement is to replace the room stat with a
programmable stat. You can than set your existing timer to switch the hot
water on and off at the times you wish - and switch the heating to
continuous (manual). The heating will then actually be controlled by the
programmable stat - which enables you to have different temperatures at
different times should you so wish, as well as being OFF when required.

Would this mean that the hot water would be on whenever the
programmable stat called for heat ???

Any ideas which stat I could use, the current one is an old brown
honeywell thing with no model number on (or in) it. I could take a
photo of it and the small wiring diagram that is on the inside of it,
and upload it on the web somewhere ??

Cheers.

P.S please excuse any typos, in a bit of a rush !